Single vs. Double Quotes in PostgreSQL Queries: When to Use Which?

Usage of single quotes and double quotes in PostgreSQL

PostgreSQL beginners often encounter the problem of using quotes in queries. Both single and double quotes can be used to enclose values, but their functions are different.

When to use double quotes

Double quotes are mainly used to specify identifiers, such as table names and column names. In the following query:

select * from employee where employee_name="elina";

Both the table name "employee" and the column name "employee_name" should be enclosed in double quotes. However, in most cases, PostgreSQL allows the omission of double quotes around identifiers unless the identifier contains spaces or special characters.

When to use single quotes

On the other hand, single quotes are used to enclose string constants. In your example:

select * from employee where employee_name='elina';

The value 'elina' is a string constant and must be enclosed in single quotes.

Use of double quotes in other contexts

While double quotes are primarily used for identifiers, they can be used for other purposes as well:

• Identifier quoting: Double quotes can be used to force PostgreSQL to treat a string as an identifier, even though it would not normally be treated as an identifier. This is useful for situations involving keywords or reserved names.
• Delimited Identifier: Double quotes can be used to create a delimited identifier, allowing you to use reserved names or names that contain special characters.
• Dollar-quoted string: In a dollar-quoted string (for example, ${double_quoted_string}$), double quotes can be used to represent literal double quotes within the string.

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